Configurable DSL modem for high bit rates

ABSTRACT

A method for configuring a multi-port digital subscriber line (DSL) modem, the method begins by utilizing frequency bands of a single DSL channel to support a data communication when loop length of the single DSL channel and data rate of the data communication are favorable. The method continues by utilizing some of the frequency bands of the single DSL channel and frequency bands of at least one other DSL channel to support the data communication when the loop length of the single DSL channel is unfavorable or the data rate of the data communication is unfavorable.

This patent application is a continuation under 35 USC § 120 to patentapplication entitled CONFIGURABLE MULTI-PORT MODEM TO ACHIEVE A HIGH BITRATE IN A DSL SYSTEM, having a Ser. No. 10/200,991, and a filing date ofJul. 23, 2002 now U.S. Pat. No. 6,754,318.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to communication systems and moreparticularly to digital subscriber line (DSL) based communicationsystems.

2. Description of Related Art

Communication systems are known to enable a plurality of communicationdevices to communicate among themselves and with communication devicesin other communication systems. Such communication devices, which may becomputers, modems, facsimile machines, printers, personal digitalassistants, et cetera, communicate voice, text, and/or video data. Suchcommunication systems support the communication of data in accordancewith one or more communication standards. As is known, there are a largenumber of communication standards for the communication of data and suchstandards vary from country to country. For example, there are a varietyof standards governing digital subscriber line (DSL) communications andsuch standards vary from country to country.

As is further known, for a communication device to communicate via a DSLbased system, the communication device includes a DSL modem. Typically,the location of the communication device with its associated DSL modemis referred to as the customer premises. The DSL modem at the customerpremises is typically coupled via a twisted pair to a DSL modem at acentral office. FIG. 1 illustrates an example of a DSL modem at thecustomer premise (CPE) coupled to a DSL modem at the central office(CO). The coupling is achieved via a twisted pair, which supports oneDSL channel, and is one of a plurality of twisted pairs in a cablebinder, or bundle of wires. In this example, the frequency allocation ofthe DSL channel is illustrated in FIG. 2.

As shown in FIG. 2, the DSL channel includes 4 frequency bands (band 1through band 4). Each band may be allocated for upstream transmission(i.e., from the CPE to the CO) or downstream transmission (i.e., fromthe CO to the CPE). For example, bands 1 and 3 may be used for upstreamtransmissions while bands 2 and 4 are used for downstream transmissions.The width (i.e., frequency) and height (i.e., power) of each band mayvary and are typically defined by one or more standards. For example,various DSL standards prescribe a frequency, or spectral, plan thatdefine the transmit frequencies (i.e., start frequency and width) andassociated powers (i.e., height) for each band. This is done primarilyto minimize near-end-cross-talk between twisted pairs within a cablebinder by having each twisted pair within a cable binder using the samefrequency plan.

To support the DSL channel illustrated in FIG. 2, the CO modem and CPEmodem of FIG. 1 each include two transmitters and two receivers. Inaddition, each modem includes a hybrid, which performs a 2-wire to4-wire conversion, a summer, and a splitting multiplexer and areconstruction multiplexer. Accordingly, for the example given wherebands 1 and 3 are used for upstream data communications, the 1^(st)transmitter of the CPE modem transmits the data in band 1 and the 2^(nd)transmitter of the CPE modem transmits the data associated with band 3.The transmitters in the CO modem transmit the data in band 2 and data inband 4, respectively. Correspondingly, the receivers in the CPE modemreceive the data in band 2 and band 4, respectively. Similarly, thereceivers in the CO modem receive the data in band 1 and band 3,respectively. Alternatively, bands 1 and 3 may be used for downstreamtransmissions and bands 2 and 4 may be used for upstream transmissions.

The splitting multiplexers in the CO modem and CPE modem split theincoming transmit data between the respective transmitters. Conversely,the reconstructing multiplexers, reconstruct the data received from therespective receivers into a serial data stream.

When data can be allocated into all 4 bands, the CPE modem and CO modemare capable of transceiving data at a relatively high bit rate (e.g.,greater than 5 Mbps). Typically, the shorter the twisted pair, the lesscable loss and the less cross-talk the twisted pair, or loop, exhibits.Conversely, the cable loss and cross-talk increase as the length of theloop increases. When the cable loss and cross-talk increase tosignificant levels, the upper frequency bands (e.g., band 3 and band 4),become unusable. Thus, CPE modems coupled to the central office viashorter loops typically have higher bit rates than CPE modems coupled tothe central office via longer loops. This creates a discontinuity inquality of service since some users have a higher bit rate than others.

Therefore, a need exists for a method and apparatus for a configurablemodem that achieves high bit rates in a DSL system regardless of theloop length.

BRIEF SUMMARY OF THE INVENTION

The configurable DSL modem of the present invention substantially meetsthese needs and others. In one embodiment, a method for configuring amulti-port digital subscriber line (DSL) modem, the method begins byutilizing frequency bands of a single DSL channel to support a datacommunication when loop length of the single DSL channel and data rateof the data communication are favorable. The method continues byutilizing some of the frequency bands of the single DSL channel andfrequency bands of at least one other DSL channel to support the datacommunication when the loop length of the single DSL channel isunfavorable or the data rate of the data communication is unfavorable.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic block diagram of prior art DSL modems;

FIG. 2 is a graphical representation of frequency band allocations of aDSL channel in accordance with one or more DSL communication standards;

FIG. 3 is a schematic block diagram of a DSL system in accordance withthe present invention;

FIG. 4 is a schematic block diagram of a configurable modem inaccordance with the present invention;

FIG. 5 is a graphical representation of an example of frequency bandusage in the DSL system of FIG. 3;

FIG. 6 is a graphical representation of a 2^(nd) example of frequencyband usage in the DSL system of FIG. 3;

FIG. 7 is a graphical representation of a 3^(rd) example of frequencyband usage in the DSL system of FIG. 3;

FIG. 8 is a schematic block diagram of an alternate configurable modemin accordance with the present invention; and

FIG. 9 is a logic diagram of a method for configuring a multi-port DSLmodem in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 is a schematic block diagram of a DSL system 10 that includes aplurality of configurable modems 20–26 at various customer premises(CPE1–CPE4) and a central office (CO). The central office includes aplurality of configurable modems 12–18. Each configurable modem 12–18 ofthe central office is coupled via a plurality of twisted pairs with aconfigurable modem 20–26 at one of the customer premises CPE1–CPE4. Thetwisted pairs between the central office and the customer premises maybe in one or more bundles of twisted pairs, or cable binders and mayinclude two or more twisted pairs.

Each of the configurable modems 20–26 at the customer premises CPE1–CPE4communicates DSL signals 28–34 with a corresponding configurable modem12–18 within the central office. For example, configurable modem 20processes user data 1 to communicate DSL signals 28 with configurablemodem 12. Similarly, configurable modem 22 processes user data 2 tocommunicate DLS signals 30 with configurable modem 16. Configurablemodem 24 processes user 3 data to communicate DSL signals 32 withconfigurable modem 14. Configurable modem 26 processes user 4 data tocommunicate DSL signals 34 with configurable modem 18.

The distance between the central office and each of the customerpremises may range from a few hundred feet to several kilofeet.Accordingly, the customer premises that are closer to the central officehave a shorter DSL loop than customer premises that are further away.However, by including the configurable modems 12–26, the same high bitrate of service may be provided to each customer premises regardless ofthe loop length. To achieve this, the configurable modems 20 may beimplemented as shown in FIG. 4 and/or in FIG. 8.

FIG. 4 is a schematic block diagram of a configurable modem 12–26 thatincludes multiplexers 40 and 42, a plurality of transmitters 44–48, aplurality of receivers 50–54, a switching module 56, and a plurality ofhybrids 58–64. Each of the plurality of hybrids is coupled to acorresponding one of twisted pairs 66–70. The hybrids 58–64 perform a2-wire to 4-wire conversion. As shown, the 2-wire connection is to thetwisted pair and the 4-wire connection is to the switching module 56.

The switching module 56 couples one or more of the transmitters andreceivers to individual hybrids based on a configuration control signal72. For example, if the loop length is very short, all frequency bandsof a DSL channel that includes multiple frequency bands are usable. Assuch, a single twisted pair may be used to support a DSL communicationand provide a high bit rate. For example, hybrid. 58 via twisted pair 70may support the DSL channel having multiple frequency bands (e.g., sixfrequency bands). When this is the case, the switching module 56 coupleseach of the transmitters 44–48 to hybrid 58 and also couples each of thereceivers 50–54 to the hybrid 58. With this configuration, eachtransmitter and each receive is allocated a frequency band.

For the example of short loop length and a six frequency band channel,FIG. 5 illustrates one possible allocation of the frequency bands. Inthis illustration, bands 1, 3, and 5 are allocated for upstreamcommunications and bands 2, 4, and 6 are allocated for down streamcommunications. If the configurable multi-port modem is contained at acustomer premises, transmitter 44 may be allocated to process frequencyband 1; transmitter 46 may be allocated to process frequency band 3; andtransmitter 48 may be allocated to process frequency band 5. Further,receiver 52 may be allocated to process frequency band 2; receiver 50may be allocated to process frequency band 4; and receiver 54 may beallocated to process frequency band 6. In this example, twisted pairs 66and 68 are unused.

As the loop length increases, and the number of frequency bandsdecreases, the configuration control signal 72 may instruct theswitching module 56 to use a pair of hybrids. This example isillustrated in FIG. 6 where the high frequency bands of twisted pair 70are unusable due to the loop loss and/or cross-talk of twisted pair 70.As such, twisted pairs 68 and 70 are used to support a DSLcommunication. In this example, the switching module 56, based on theconfiguration control signal 72 would couple transmitters 44 and 46 tohybrid 58 and couple transmitter 48 to hybrid 60. In addition, theswitching module 56 would couple receivers 50 and 52 to hybrid 58 andreceiver 54 to hybrid 60.

Depending on whether the configuration modem is at the central officesite or at a customer premises, the allocation of transmitter andreceiver for upstream and downstream communications would vary. Forexample, if the modem were at a customer premise site, the transmitters44 and 46 would be allocated to bands 1 and 3 of twisted pair 70.Receivers 50 and 52 would be allocated band 2 and band 4 of twisted pair70. Transmitter 48, which is coupled to hybrid 60, would be allocatedband 1 of twisted pair 68 and receiver 54 would be allocated band 2 oftwisted pair 68.

When the loop length between the customer premise and central office isof such a length where the losses only allow bands 1 and 2 to be used,the configuration control signal 72 causes switching module 56 to useeach of the hybrid 58–64. Such an example is illustrated in FIG. 7 whereeach of the twisted pair 66–70 is used, but only bands 1 and 2 of therespective twisted pairs are used. Accordingly, if the configurablemodem of FIG. 4 is at the customer premise, transmitter 44 and receiver50 would be coupled to hybrid 58 and allocated bands 1 and 2 of twistedpair 70, respectively. Transmitter 46 and receiver 52 would be coupledto hybrid 60 and allocated bands 1 and 2 of twisted pair 68,respectively. Transmitter 48 and receiver 54 would be coupled to hybrid64 and allocated bands 1 and 2 of twisted pair 66, respectively.

Accordingly, the bit rate supported by the configurable modem 12–26 canmaintain a high rate by utilizing one or more twisted pairs asillustrated in examples 1–3 depicted in FIGS. 5–7. As one of averageskill in the art will appreciate, more or less twisted pairs, hybrids,transmitters and receivers may be included in a configurable modem toachieve higher bit rates or lower bit rates than the bit ratesachievable with the 3 sets illustrated in FIG. 4 and correspondingexamples of FIGS. 5–7.

Returning to the discussion of FIG. 4, the configurable modem 12–26 alsoincludes a splitting multiplexer 40, or demultiplexer, that splitsoutbound data 74 amongst the plurality of transmitters 44–48. Theconfigurable modem 12–26 also includes a multiplexer 42 that combinesthe received data via receivers 50–52 and reconstructs a serial inbounddata 72. The generation of the configuration control signal 72 will bedescribed in greater detail with reference to FIGS. 8 and 9.

As one of average skill in the art will appreciate, the switching module56 may be implemented using jumper wires, switches, or other manualcoupling means. In these instances, the configurable control signal 72is implicit in the coupling of the jumper wires and/or the configuringof the switches. As one of average skill in the art will furtherappreciate, the number of bands supported by a DSL channel may be moreor less than the six discussed with reference to FIGS. 4–7. For example,in one embodiment, four bands may be used.

FIG. 8 is a schematic block diagram of an alternate embodiment of theconfigurable modem 12–26. In this embodiment, the configurable modemincludes combining multiplexer 86, splitting multiplexer 88, splittingmultiplexer 40, combining multiplexer 42, a plurality of transmitters44–48, a plurality of receivers 50–54, a transmit switch module 80, areceive switch module 82, a plurality of hybrids 58–64, and a controlmodule 84. The control module 84, which may be included in the modem ofFIG. 4, includes a processing module 90 and memory 92 to generate theconfiguration control signal 72. The processing module 90 may be asingle processing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on operationalinstructions. The memory 92 may be a single memory device or a pluralityof memory devices. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, and/or any device that storesdigital information. Note that when the processing module 90 implementsone or more of its functions via a state machine, analog circuitry,digital circuitry, and/or logic circuitry, the memory storing thecorresponding operational instructions is embedded with the circuitrycomprising the state machine, analog circuitry, digital circuitry,and/or logic circuitry. The memory 92 stores, and the processing module90 executes, operational instructions corresponding to at least some ofthe steps and/or functions illustrated in FIGS. 8 and 9.

The functionality of multiplexers 40 and 42, transmitters 44–48,receivers 50–54 and hybrids 58–64 operate as previously discussed withreference to FIG. 4. The transmitter switching module 80 and receiverswitching module 82 provide selective coupling between hybrids 58–64 andtransmitters 44–48 and receivers 50–54, respectively. Accordingly, thetransmit switching module 80 and receiver switching module 82 may be aplurality of transistors, switches or combinations thereof that provideselective coupling between the transmitters 44–48 and hybrids 58–64 andreceivers 50–54, respectively.

In this embodiment, the configurable modem may support multipleconnections (three are shown, but more or less may be supported). Aconnection is a data communication by an in-office or in-home devicethat includes a configurable DSL modem with a configurable DSL modem atthe central office. Accordingly, if the loop length between the DSLmodem at the customer premises and central office is short, threeconnections may be supported. To support the three connections, eachhybrid is coupled to a single receiver and a single transmitter or a setof receivers and a set of transmitters depending on the desired bitrate. Accordingly, to achieve the highest bit rate possible, each hybridwould be coupled to multiple receivers and transmitters to processmultiple bands of the DSL channel. As such, for a six band DSL channeland three twisted pair modem, the modem may include up to ninetransmitters and nine receivers to support the highest bit rate possiblefor each of three connections.

As the loop length increases and the higher frequency bands becomeunusable, the configurable modem 12–26 may be reconfigured to support 1or 2 connections. When 1 connection is being supported, the configurablemodem 12–26 functions similarly to the modem of FIG. 4 and thecorresponding example illustrated in FIG. 7. When 2 connections aresupported, the transmitters 44 and 46 and receivers 50 and 52 may beallocated to one of the two connections and transmitter 48 and receiver54 may be allocated to the other of the two connections. Accordingly,the control module 84 determines the appropriate configuration andgenerates the configuration control signal 72 based thereon.Alternatively, the configuration control signal may be determined bymeasurements at the CPE and the switching module implemented via jumperwires and/or switches.

FIG. 9 is a logic diagram of a method for configuring a multi-port DSLmodem in accordance with the present invention. The process begins atStep 100 where a desired data bit rate for a connection is determined.The data bit rate may range from a few hundred kilobits per second totens of megabits per second. The process then proceeds to Step 102 wheredata capacity for frequency bands of a DSL channel supporting theconnection are determined. Such a determination may be based ondetermining the loop length of the connection and based on the looplength establishing the data capacity. For a detailed discussion ondetermining loop length, refer to co-pending patent application entitledADJUSTMENT OF TRANSMIT POWER BASED ON AN ESTIMATED ELECTRICAL LENGTH OFA LOOP, having a provisional filing date of May 31, 2002 and Ser. No.60/384,469. As previously mentioned, as the loop length increases, looploss increases as does cross-talk. Thus, the greater the loop loss andcross-talk, the less usable the higher frequency bands are.Alternatively and/or in addition to loop length estimations, signal tonoise ratio may be used to determine the data bit rate.

The process then proceeds to Step 104 where a number of twisted pairs tosupport the connection is determined based on the desired data bit rateand the data capacity for the frequency bands. This was graphicallyillustrated and described with reference to FIGS. 5–7. The process thenproceeds to Step 106 where at least one transceiver (i.e.,transmitter/receiver) is allocated to a frequency band pair (band 1 forupstream, band 2 for downstream) for each number of twisted pairs. Suchan allocation may be done as graphically illustrated and described withreference to FIGS. 5–7.

The preceding discussion has presented a method and apparatus forconfiguring a multi-port DSL modem to achieve a high bit rate.Accordingly, such a configurable multi-port DSL modem provides the samequality of service, i.e., high bit rate, to each customer regardless ofthe loop length between the customer premise and the central office. Asone of average skill in the art will appreciate, other embodiments maybe derived from the teaching of the present invention, without deviatingfrom the scope of the claims.

1. A method for configuring a multi-port digital subscriber line (DSL)modem, the method comprises: utilizing frequency bands of a single DSLchannel to support a data communication when loop length of the singleDSL channel and data rate of the data communication are favorable; andutilizing some of the frequency bands of the single DSL channel andfrequency bands of at least one other DSL channel to support the datacommunication when the loop length of the single DSL channel isunfavorable or the data rate of the data communication is unfavorable.2. The method of claim 1 further comprises: determining data capacityfor the frequency bands of the single DSL channel based on the looplength of the single DSL channel; and when the data rate of the datacommunication exceeds the data capacity of the frequency bands of thesingle DSL channel, determining that the loop length of the single DSLchannel and data rate of the data communication are unfavorable.
 3. Themethod of claim 1 further comprises: allocating at least one of thefrequency bands of the single DSL channel for downstream data; andallocating at least one other of the frequency bands of the single DSLchannel for upstream data.
 4. The method of claim 1, wherein theutilizing some of the frequency bands of the single DSL channel andfrequency bands of at least one other DSL channel to support the datacommunication comprises: utilizing frequency bands of a second DSLchannel as the frequency bands of the at least one other DSL channelwhen loop length of the single and second DSL channels and the data rateof the data communication are favorable; and utilizing some of thefrequency bands of the second DSL channel and frequency bands of a thirdDSL channel as the frequency bands of the at least one other DSL channelwhen loop length of the single and second DSL channels and the data rateof the data communication are unfavorable.
 5. An apparatus forconfiguring a multi-port digital subscriber line (DSL) modem, theapparatus comprises: processing module; and memory operably coupled tothe processing module, wherein the memory includes operationalinstructions that cause the processing module to: utilizing frequencybands of a single DSL channel to support a data communication when looplength of the single DSL channel and data rate of the data communicationare favorable; and utilizing some of the frequency bands of the singleDSL channel and frequency bands of at least one other DSL channel tosupport the data communication when the loop length of the single DSLchannel is unfavorable or the data rate of the data communication isunfavorable.
 6. The apparatus of claim 5, wherein the memory furthercomprises operational instructions that cause the processing module to:determine data capacity for the frequency bands of the single DSLchannel based on the loop length of the single DSL channel; and when thedata rate of the data communication exceeds the data capacity of thefrequency bands of the single DSL channel, determine that the looplength of the single DSL channel and data rate of the data communicationare unfavorable.
 7. The apparatus of claim 5, wherein the memory furthercomprises operational instructions that cause the processing module to:allocate at least one of the frequency bands of the single DSL channelfor downstream data; and allocate at least one other of the frequencybands of the single DSL channel for upstream data.
 8. The apparatus ofclaim 5, wherein the memory further comprises operational instructionsthat cause the processing module to utilize some of the frequency bandsof the single DSL channel and frequency bands of at least one other DSLchannel to support the data communication by: utilizing frequency bandsof a second DSL channel as the frequency bands of the at least one otherDSL channel when loop length of the single and second DSL channels andthe data rate of the data communication are favorable; and utilizingsome of the frequency bands of the second DSL channel and frequencybands of a third DSL channel as the frequency bands of the at least oneother DSL channel when loop length of the single and second DSL channelsand the data rate of the data communication are unfavorable.